turntable mat : boston mat, audioquest sorbogel ma

These are two (very) different mats, so your post is pretty confusing. Can you clarify? For starters, what turntable are you considering?

I m considering VPI HRX or Kuzma Reference. TQ

Still don't know what mat(s) you're talking about. The Boston Audio mat is pure graphite and quite hard; the AQ one is soft. In any event, why not wait until you get the turntable and try them both?

I can only speak from my own experience. I had replaced the stock mat (The Groove Isolater)on my Oracle some years back with an Audioquest sorbatane mat. I purchased a The Mystic Mat two months agoand it really opened up the extension on my analog front end. They say not to use it with a clamp unless the record slips while playing it and so i didn't clamp it. After a couple of days I said what the hell and clamped it and it added more bass to my Oracle.So you see you do what sounds good in Your system. Whomever you buy from see if they have a LOAN mat to try before you buy.