Well, since you have not gotten any responses as yet, I will give you my semi-second hand impressions. (I say semi-second hand, as I did not own them, but my friend owned the VTL 450's for a year or so, before he bought the hybrid Lamm M2.2 monoblocks. A couple of years later he tried out the VAC Phi 300 (not the upgraded 300.1 version though), and then compared it to the Lamms. I did get to hear the VTLs a few times in his system, and I was there for the VAC to Lamm comparision - lucky me! :-)
First off, the VTL 450's are very fine amps, and for the money, a good deal. (Used they tend to go for around $4,500.) They have plenty of power, and good bass response. (Great bass response when you consider that they are tube amps.) For tube amps they are pretty neutral, without a lot of mid-range bloom. They do run hot though, so consider that they will probably raise the room temperature several degrees. (The Lamms run cooler, although even they run very warm, but not hot. but even they will raise the room temperature a few degrees.) When compared to the Lamm M2.2s, they compare favorably in the mid-range (both are fairly neutral), in the treble, the Lamms are slightly more extended and detailed. In the bass response, the Lamms are incredible, whereas the VTLs are merely good. Both soundstage and image very well. (FYI, my impressions of the VTLs are based upon my recollections from a couple of years ago.) All in all, while the VTLs are good amps, the Lamms are great amps, but since they cost at least double the cost of the VTLs, that should be expected. The speakers for this comparison were the Avalon Eidolons, and the preamp was a ARC Ref. 2, mk. 2. IMHO, the ARC Ref. 2 is a very good preamp, but not a great preamp, as I felt it had a bit too much tube noise. I will point out that I am VERY sensitive to tube noise, which is one reason I have a solid state preamp, the Ayre K-1xe. FYI, it was during the comparison of the VTL to the Lamm amps, that I fell in love with the Lamm amps, and quickly managed to buy a used pair of Lamm M2.1 hybrid monoblocks, which I still have. :-)
When comparing the VAC Phi 300 to the Lamm M2.2s, this was a much closer comparison. (Of course it should be, as the price of an used VAC is about $8K, compared to the used price of the Lamms which is about $12K.) In fact, I would say it was a coin flip as to which one is better. The bass response of the VAC is very similar to the VTL - good, but not great. The treble response is better than the VTL, in fact, it is even slightly better than the Lamm M2.2s. The mid-range of the VAC is very sweet. (I don't think it is as neutral as the Lamms, but given how sweet it is, who cares!!!) There is one other item we noticed, which actually is the reason my friend ended up keeping the Lamms, rather than changing to the VAC, is that the VAC seemed to be a little slower on the initial attack of percussive instuments, such as drums or even the initial key/hammer on the piano strings. (It was barely noticable, but it was there, nonetheless. I think the VTL also had this same trait.) My friend told me that if he could have afforded to own both amps, he would have bought the VAC. (But the economy has affected him too.) All I know, is that we both sat quietly and throughly enjoyed listening to an entire album side of Norah Jones singing, without either of us speaking. The mid-range of the VAC has an enchanting quality that puts it up there with any amp I have ever heard. (However, the VAC is also one of the hottest running amps I have ever known as well. It put out at least as much heat as the VTL, and more than both Lamm monoblocks put together.)
The equipment for this round of comparisons, included the Rockport Antares speakers, and the ARC Ref. 3 preamp. I much prefer the Ref. 3 preamp to the Ref. 2, as it is much quieter. I would have no problem owning the Ref. 3. It is also possible that the VAC has slightly better bass response than the VTLs, as the Antares are a somewhat difficult speaker to drive, due to its 13" woofer. The VAC did a very good job, just not a great job. The VTL only had to drive the 11" woofer of the Avalon Eidolon.
My opinion is that if you can afford the VAC Phi 300, go for it. It is a better amp than the VTL 450s, but for double the price, it should be. If you need to save some money, the VTLs are good bang for the buck amps, IMHO.
Well, those are my two cents worth.
Good Luck in your search.