So messing around with my GI and M3 mags I noticed something about the difficulty to strip the round.

On GI mags there is considerably more friction and force required to strip a round when compared to Pmags.

So this got me wondering, does that increased resistance lead to slower bolt velocity on the forward stroke?

Would it be enough to turn an already sluggish rifle(for whatever reason) into a FTF gun?

Have any tests been done in regards to bolt velocity when chambering from different magazine materials?

of course ! Any drag or increased pressure on any number of moving parts could cause a malfunction.
Magazines are the very first thing you look at when things go side ways. Spring, feed lip, follower, mag catch, ding, dent, crack (plastic)...

Yes but the amount of drag is considered in the design of the rifle.

When the M16 was analyzed during the Viet Nam war (Ichord Report) I do not believe any blame was placed on the magazine.  There was also a fairly large study of the  weapons used in Iraq in 2006 and it was not mentioned as being a problem. Slippery is not always better, in some designs friction is a factor in how the weapon functions( read about Gen Thompsons obsession with the Blish Principle when designing the TSMG)