I have a TipX, and used a friends 8.1.
8.1 was nice, hefty in the hand because of the mags, the trigger for me was awful (I hate it straight! Feels so... tacky!) and I couldn't easily aim it, to be honest...
Got a TipX on an impulse buy. Felt much less bulky in the hand, sleeker, and more durable somehow. Loved my TipX, so I've kitted it out.
It has a remote line adapter, to run off a small HPA tank rather than co2 cartridges, First Strike block to shoot 68cal and FS. ZetaMag and 4 Tru-feed mags, modded for FS. FazMags to hold the clips.
Oh that's another thing! The price of the mags for the Tib put me off... Didn't really feel an advantage to having loads of co2 stashed in mags, lost count so easily in what went where...
Hope this helps.