Misread an acronym. Too many G's but whatev.
As far as I know you can buy Game Pass with whatever funds you have in you MS balance. Only way it differentiates funds is MD Rewards redemption funds have a 90 day expiration.
If using MS Reward points it's a better ratio to purchase Game Pass directly with reward points, I believe.
I was gonna shop for more ultimate codes, but I maxed out at 3 years gold before converting to ultimate and have been getting a free month code every three months for their Ambassador program, so still have 2 years and 3 months left and haven't been many good deals.
Codes are only getting more expensive, though, so might be worth stocking up if there is a good deal (though will prob just redeem time through reward points if my sub gets short).
MS Gift cards are where the good value is, so I try to find those deals. Bought $300 worth a few years ago with 25% off that made me feel good buying games 75% off with those funds.