Suggested power tubes for Onix SP3 integrated amp?

Hello- I finally dialed in all of the minitubes for my SP3, a combination of vintage RCA's and Amperex 6922's. Now I'd like to upgrade from the stock Melody 5881 power tubes to something better. SED 'flying c" 6L6GC's and VA 350B's are under consideration, but honestly I'm not sure what's worked for others out there and the 6L6 universe is pretty foreign to me. Any suggestions?
Thanks for the help!
I don't have extensive experience with the 6L6/5881's but I've been very happy with vintage Tung-Sol 5881's. I haven't tried the reissue Tung Sol's but the originals are very plentiful. Many are well-used but if you're patient you should be able to find a quad that are NOS or test very strong. They don't command the atmospheric prices of a lot of older tubes, I'm sure because they are quite common. I've found several nicely matched quads at between $50 and $150.

In my AES/Cary AE-25 amp they are very musical and 'organic,' a pleasure to listen to.

Another interesting alternative is the early 80's Russian 6p3s-3, an equivalent to the 5881. I don't think they're quite as nice as the early Tung-Sol in my amp but they're ridiculously inexpensive from several sellers on ebay. They've been discussed extensively on audioasylum and the consensus is that the pre-1984 coin-base tubes are the ones to get. I've bought three quads online and they're definitely worth experimenting with.
Thanks so much for the input. I'll have to do more investigating and will likely try the 6p3s-3's just for fun. And I have heard many good things about vintage Tung Sols.
Happy listening!
When you get your new power tubes then you can start on the signal tubes again!!! What a hobby,gotta love it.