tt steel frame upgrade

Hi, I'm Thorsten from Hamburg. Since one year ago I'm driving a Raleigh competition based TT bike and already made 2500km with it. In general I feel very comfortable with, I can really ride about 3 hours on the extension.
I also joint one completion wit it. I have used a powermeter at this event and it turned out that it cost approximately 20-30 extra watts at 40km compared to a modern bike.
In think the biggest issue is that it doesn't allow me a more aggressive position on bike. Due to the size head tube I can't move the handlebars further down.
Fort this reason I think in replace this frame with a lopro. Unfortunately I hove no knowlage about this frames. I need some advice what I have to looking for.
This current is 57cm (c-t) , head tube 15cm a top tube 56.5cm I think. I might need a frame with a sloping towards the head tube.
Any hints what I could choose and is not very expensive. I no look for fancy brands, it just need to be functional.
One other point, if possible I want to get rid of stem adapter, but I have now idea if quill stems exist with a small extension angle.

Thx for any hints
Thorsten

I think with modern frames it is best to go a size smaller in terms of seat tube while trying to keep the top tube length constant. You will have more seat post sticking out and you can change height at the front using spacers.
Might be worth checking out the TT section for more advise:

https://www.lfgss.com/conversations/142537/?offset=9475#comment12303037

If you want to keep it "vintage" you could of course go for a lo pro. Check out Scilly Suffolks Lo Pro here

https://www.lfgss.com/conversations/263688/

although no sloping tt ;)

Lo pros come up in the classifieds every now and then.
Nice example here,

https://www.lfgss.com/conversations/267730/

In terms of sizing it can be a bit difficult. Since they have a sloping top tube you should look at effective (or virtual) top tube length but it's probably best to try the geo out first

Yes, the roberts is what I looking for. Is just a little bit to big. Yes in sizeing I'm not sure at all. All i know is that my current top tube is perfect, so effective top tube should be near to this.
I looking not explicitly for a vintage, but for this classic thin steel tubes.

Thank for thins link, now i have to read a bit :)

Finally I found a Sirius lo pro frame in classifieds. Now it replaced the old raleigh frame. Now is my default training TT bike, while in race I use PlanetX Exocet 2. Both bikes have very similar setup

Nice! I was tempted to buy that myself ;)