hoakypoaky, you and I must be walking a similar path:
I used Comet LEDs as well. They're local to me (they're in Boulder, CO and I live in Broomfield, about 12 miles away) and discovered them after meeting co-owner Ryan at a local tournament a couple years ago. Now I bump into him at all sorts of tournaments and shows in the Denver area - they're really nice people over there at Comet. Best of all....since they're just across town, buying from them online I get next day shipping at USPS First Class pricing unless I drive over there to pick up my order.
After doing the hardtop last year, I went with 2SMD Cool Whites for the topside GI and 2SMD Natural Whites for the white inserts and color matched the other inserts. Like you, I put a different color (Blue for me) behind the 5x insert because I wanted it to stand out. I just did the same color matching (Green 2x, Yellow 3x, Blue 5x) on my Black Jack project last night.
I also put an RGB color changing LED behind the candelabra and the baron's head on the backglass (saw and liked that on Todd Tuckey's TNT MH video) and another RGB for the credit light on the apron.
I also went with the disc LEDs in the pop bumpers....I too like they way they illuminate the bumper bodies along with the cap (I did the same in the pop bumpers for Black Jack and the one pop in my Black Knight). And to top off that coincidence, I also switched the pop bumper sockets to 555 when I rebuilt them! Love the bayonets for inserts and GIs, hate them in pop bumpers.
Last month, I decided to try #47 incans for the MH topside GI and I must say, I really, really like that look. While the Cool White LEDs were nice, the #47 incans really brightened up the playfield without being overwhelming. I think I'm going to stick with that....they don't run as hot as #44's and since this is HUO and turned on for only a few hours several times a week, I'm not too worried about warping or marking up the plastics with burn spots.
Looking forward to seeing more photos when you complete your project. I'd take some shots of mine with the "updated" #47 incans topside but not sure a photo would capture how good it really looks.