Two subs - should they be the same size or is different ok

I don’t think it’s a huge deal that the subs are different sizes as long as each is properly placed in the room and dialed in.  Not sure about using different crossover frequencies, but I suppose it never hurts to try and it’s free so why not?  For me, there’s a frequency where your Studios will begin to roll off and you want to integrate the subs there as seamlessly as possible.  Here’s a very practical method to dial in a sub that is supposedly based on tips from Paradigm, and they make common sense to me so I’d start with this as a baseline for both subs and then experiment with goosing up one of the subs crossover to see if it’s an improvement or not.  Anyway, here’s the procedure…

1. Turn the Subwoofer Level control completely counterclockwise to its minimum; 2. Turn the Subwoofer Cut-Off Frequency control clockwise to its highest frequency (i.e. 150 Hz). 3. Set the Phase Alignment Control to 0°; 4. While you listen to a bass music or video selection in your primary listening area, have an assistant turn up the Subwoofer Level control until the subwoofer can be clearly heard; 5. Have an assistant try the Phase Alignment control until you hear the most bass. Your subwoofer and front speakers are now in phase. Do not change phase alignment again unless you move the subwoofer or the front speakers to a different location in the room or move or remove large items of furniture or room furnishings (i.e. carpet, draperies, etc.) 6. Turn the Subwoofer Level control completely counterclockwise to its minimum. 7. Turn the Subwoofer Cut-Off Frequency control completely counter-clockwise to its lowest frequency (i.e. 50 Hz); 8. Slowly rotate the Subwoofer Level control until you match the subwoofer output level with the level of your front speakers. Bass should be clearly audible, but not intrusive; NOTE: If using an A/V receiver or processor to control crossover setting, skip the next step and set the subwoofer cutoff frequency control to ‘Bypass.’ 9. Slowly rotate the Subwoofer Cut-Off Frequency control until you hear the best subwoofer/main speaker blend. If the sound is too ‘thin,’ you have not set the frequency high enough; if the sound becomes ‘boomy’ you have set the frequency too high. Adjust until you find the most natural balance.  The sub should not draw attention to itself.

Don’t neglect subwoofer placement, and you’d obviously wanna optimize this first before performing the above tuning procedure.  Use the Crawl Method to find the best spots for your subs in your room, but failing that placing the subs at the midpoint of either the left/right or front/back walls can be effective and much better than just plopping them anywhere or placing them in the corners.  Here’s the Crawl Method just FYI…

https://www.audioholics.com/home-theater-connection/crawling-for-bass-subwoofer-placement

Hope this helps, and best of luck. 

Is your room dedicated to music only?

Why take unnecessary chances?  Just go with matching subs and be done with it.  You'll have greater peace of mind knowing everything in your audio system is perfectly balanced.  That would be my recommendation.  Happy listening.

Slaw... yes, I do have a tv with soundbar but music first.  I want it optimal for 2 ch stereo

Since you have both already, no harm in trying them.  As mentioned, the key is placement and dialing them in.  

While setting up current system 'bout 3 or 4 years back I experimented with none, one and a pair of subs. A pair in a two channel system is a no brainer regardless of whether same brand and/or size. My "listening room" is this thing called a living room which I share with my wife. Size was a consideration when going for the second sub. I currently have a REL T/7i and T/5i. No complaints.

There is no advantage to different crossover points. In your case you will have slightly less out put of note C2 at 65.406 Hz. Gain levels should be close which can be more challenging with mis-matched subs.

According to Revel the Studio 2's  3 db down point is 32 Hz. Normally for best results your crossover point should be in that vicinity.  Usually, slightly lower. The goal is to try and create a quasi 1st order crossover (6 db lower at the crossover point) between your subs and mains.