Hey Scott,
Welcome to the forum.
Regarding your question about using Ampex 499, I always advise members not to use old stock Ampex/Quantegy tapes. 456 and most of their tapes made during or after that period are subject to a terrible problem called sticky shed syndrome. Sticky shed renders the tapes essentially unplayable and even if the tapes don't exhibit that problem now, they almost all will eventually. It would be one thing if new tape wasn't available but it is.
I used to use 911 but Paul Stubblebine (one of the principles here and all around tape smartguy) prefers 468. I've chosen to take his advice and I've been happy with it. If you want to save some serious cash and don't mind a few splices, contact Doc/Eileen to see if they have any deals on 10.5" pancakes that are composed of unused tape from making the Tape Project tapes. It's a killer deal IMHO.
http://www.tapeproject.com/smf/index.php/topic,824.0.htmlThe added headroom that the +9 tapes probably won't make as much difference in recording unless you're recording something like live music. Lp's have already been through enough processing so the dynamic range should "fit" onto a +6 tape just fine. Remember that most of these recordings were done on +6 or less tapes in the first place and then processed for pressing.
You'd probably reap more audible improvements by increasing the tape speed (since you stated that you're using an RS1500 you must already be recording in 1/2 track). If you do choose to use a higher output tape, I'd suggest using ATR Magnetics new tape and have your machine biased for that tape. Outside of modifying your record amp, you'll get the best results with your Technics using that tape at 15 ips.
If you really want to get the best results, don't neglect the lp side of the equation. That's half the battle after all (maybe even more). Getting your lps as clean as possible, isolating your turntable from any floor borne rumble, and having your table/arm/cartridge optimized makes a lot more difference when you expect to be listening to the recording of it over and over. Somehow, those ticks and rumbles are twice as distracting when they're always in the exact same spot.