The effect is very subtle. The thinner base gasket(s) add compression and alter port timing slightly for more low/mid. The 250s usually come with a .5 and .3 together. I usually install a single .3 at the first rebuild. What I would do in your case is keep the .5/.3 and have the head cut to correct the squish which is usually really far off with this thick a base gasket combo.
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