Yummy

Whichever stat you have less of is going to be the one that has the dominating increase (after taking into account you already have a natural 30% to crit). If you have +30% base damage already (pretty easy to get full time with BTC, troub mythical and shadow AAs), the next one percent is going to be a 1.31/1.30 increase as well.

Of course, this equality of the value of each modifier when current +base dmg = current crit multiplier is assuming 100% crit rate and not being over the +spell damage cap. If either of these is not true, x% base damage will still be better than x% crit bonus.

As brought up before (after I jumped the gun and said only the upper range would be increased), at least for necro spells sans vampire bats, the min..max results in a ratio where max/min < 1.3, meaning any crit is going to already be guaranteed over max+1. Thus, you can just consider the full effect of the modifiers rather than try and average it out on a spread of possible ranges - as lower random numbers within the original range won't result in crits that hit for higher than your current multiplier.