Given that tREF controls how frequently the memory is refreshed (to overcome charge decay,) the main issue w/ a too high tREF is you will encounter data corruption as bits start flipping from not being refreshed frequently enough (this effect is accelerated by heat.)  And since a refresh is a series of reads/writes, i would think it should not be that different from other workloads as far as the memory is concerned - if anything the core will likely be working harder as it probably doesn't have to do much during a refresh.  It is possible that a refresh is easier on the mem than your standard gaming workload due to r/w size/frequency or something like that, in which case, yes, the mem would draw more power and generate more heat as it does less refreshing and more 'real' work.

As for the 64 bios flash, it's value is really dependent on the work profile of your application/game.  For example in the mining scenario, ethereum responds well to higher bandwidth, meaning higher clocks, which require more voltage and relaxed timings (which happens to be exactly what the bios changes.)  Other coins/algorithms may respond better to lower latency, which means tighter timings possibly requiring lower clocks (and possibly less voltage,) making the bios update less useful.

I believe games in general like the higher bandwidth, so I would think the flash would be helpful, but it's probably a more delicate balance between latency and bandwidth than many mining scenarios.

EDIT: Also, in case it wasn’t already apparent, your higher mem clock (vs stock) will likely require higher core voltage for the same cclk, because the infinity fabric, which shares power with the core, runs at (roughly) the same speed as the memory.  So the increased memory voltage resulting from the bios flash isn’t the end of the story...