i’ve notice no difference in shifting between standard Deore, LX and XT. can’t imagine there would be a great deal of difference between Saint and XT.
friend at the bike shop has kitted his bike out with full XTR (because he can) and said the only piece of kit he’d keep would be the shifters. that is because you have so much play/adjustablity compared to any other shifter, nothing to do with the shifting itself. (there is a grub screw that allows more movement after being fixed to the bar)
the saints are also adjustable but not to the same extent as the XTR, just two differing positions.
i’d take which ever floats your boat asthetically. the Saint are 10 grammes more but have gold twiddly bits.