I'm new to Step Up Transformers

Please don't take what I am about to say the wrong way.  Whether an SUT would be to your liking or not is a subjective decision.  It really depends on what distortions your tastes prefer.  Everything has distortion.  Tube phono stages have different and generally higher levels of distortion than is typical for similarly priced solid state units.  Then you add an SUT and two (inlet side and outlet side) interconnects, which adds just a bit more distortion and perhaps noise as well.  Against that the SUT adds greater signal, which can improve signal to noise ratio and of course every SUT has a certain audible signature (yes that is distortion but it can be and often is pleasing to the ear).  So you see the addition of an SUT is not as simple or straight forward as it might seem at first glance.  The only way you can answer your question is to try one and let your own tastes be your guide.  No one can properly advise you beyond what I have suggested here.  This is something you have to do for yourself.  BTW, FWIW, in one of my systems I use a recently acquired Conrad Johnson ART Phono (their latest and greatest tube unit) with most often a Conolidated Silver Wire SUT although the C-J has enough gain to not need an SUT, so depending on cartridge and mood I often opt to forego the SUT.  I also have a Bob's Devices SUT which has a warmer sound and that is used too.  In my other system the phono stage is a PS Audio Stellar all solid state and it is used stand alone.  There is no right or wrong in this matter, no one size fits all circumstances, and in spite strong opinions strongly expressed in this forum and others like it, there is no one best solution.

FWIW, my favorite cartridge is a SoundSmith Hyperion, my SUTs are 10:1, but I also fearlessly interchange a variety of LOMC from Ortofon, AT (the recently introduced AT20 is quite nice), and others.  My philosophy is to try things and listen.  BTW, listen means for a while, not just for a minute or two, maybe at least an hour or more after making a change.  I like to give my ears and mind a chance to adjust to the sound of what I am trying.

"Id say wait through 2-3 listening sessions at least one hour each in length, before making any judgement of a new cartridge, and that’s only if you’re very familiar on a long term basis with the phono stage. And even then, cartridges do change over time from new, probably more so than any other piece of gear."

Yes!  This excellent advice is worth repeating for emphasis.  Thanks lewm, well said.

'I have always preferred the sound of using an SUT into the MM stage vs the built-in MC stage.'

This has generally been my experience too.

My Hyperion is a moving iron cartridge and it decidedly works best with a low gain phono stage, and my preference is to use an SUT in to the MM input of every phono stage I have tried it with. 

"Which SUT are you using with the Hyperion ?

Have you compared many ??"

My current favorite is the Consolidated Silver Wire SUT.  I also have a Bob's Devices.  Both are external and are 10:1.  I also had an internal one in my previous Conrad-Johnson phono stage.  That covers the last 10 years or so.  I've been at this a long time and have had others, Ortofon, for example, Denon too, years ago, but with different cartridges and TT/arm setups that hardly are pertinent today.  I should also mention that for several years now I have settled on Audio Sensibility Statement silver interconnects.  Interconnects in and out are pertinent and consistency is important in evaluating differences.

It sure is an expensive pursuit.  My Consolidated Silver cost $5,500, my Bob's Devices was $1,200.  I believe the Ortofon is now around $1,800.  To these prices you need to add interconnects.  It is a lot easier, cheaper and cleaner to just buy a good high gain phono stage.  My PS Audio Stellar has that capability which is why I bought it.  In fact it is what I am listening to today in my new system.  It makes more sense to join a club if possible that accommodates member loans/exchanges or at least get togethers to try different SUTs or what not.