I’m planning on getting a new frameset but don’t know which one. My spending budget is around 500-600. I plan on using it on the streets and also at the velodrome. Any suggestions?

If it were my money, I'd probably buy an All-City Big Block. Maybe an All-City Thunderdome if I wanted to spend more money and have something more track-oriented. Not an All-City shill btw. Some of the other options at that price point are just kinda weak comparatively IMO:
Dolan TC1- single-sided dropout plates are a bummer
Surly Steamroller- probably doesn't translate as well as a track bike
Planet X Carbon- makes you look Fred as ****
What I did some time ago was buy a Felt TK2 on ebay. I like everything about it except for not having waterbottle mounts for road rides and the dumb lip around the dropouts that make it annoying to get a wrench on the track nuts.

edit- Soma Rush might be a good option too

Oh yeah, looks like Planet X website doesn't have them in stock. Ehh. I've heard they're decent for track use but I wouldn't want one for anything else.

I would have to say All-City Big Block or Thunderdome too. I love them as a company and I would buy a Big Block in a heart beat if I could afford to. Also you could check out Tribe Cycles aluminum Track framesets for $359:

• Double-butted 6061 aluminum frame with a tapered headtube (1/8 - 1/2)
• Tapered carbon fork with aluminum steerer tube
• FSA Orbit headset

The Cinelli Mash Bolt 2.0 is on sale on Retrogression for $679. It's more than your budget but you know TREAT YO' SELF.

Also, another suggestion would be the Wabi Classic frameset for $450, The Wabi Special for $650, or The Wabi Thunder for $595. All of these are hand built in 'MERICA with Reynolds tubing.

the frames are hand built in Taiwan.

Yep. The completes are assembled in USA. Maybe that's where the confusion lies.

Really like my Soma Rush. The new ones come in under you budget. Nice steel and good geo. I picked my frame up for cheap on eBay. They've been making them for a long time, you might be able to find something used if you're open to that.

Nice lugs and Reynolds 531 for about $600 shipped to US...https://www.planetx.co.uk/i/q/FRHOZP...ephyr-frameset

My God why did they have to leave off bottle mounts. I'll just never understand that deal in the SS world. I don't think that one is even drilled for a rear brake.

That Holdsworth is pretty sweet looking, sizing is confusing though. Geo chart lists five sizes, but they only have small, medium, and large to choose from when ordering?