And agree 100% on Xtrader - very strange business decision to discontinue a 15 year old piece of software than thousands of users are willing to pay $1200 per month for!
Best approach may be a third option, at least as a prototype. Use Excel, with a RTD server that connects to TT. Uninstall the Bloomberg Excel Tools add-in and use direct calls into BBG's own RTD server, i.e., =RTD("BLOOMBERG.RTD","","VGA INDEX", "LAST_PRICE") instead of BDP(...) for market data (~100x faster), and you can get to an 80% solution very quickly.
re F# vs C#, I had used C# for a decade before switching (after I had a vacation ruined because of a multi-threading bug in our position-sizing model. Multi-core parallelism is much easier in F# due to default immutability). If you play around with the F# REPL you'll pretty quickly find out whether the language fits your mind well or not. For me, as soon as I read this code (http://fssnip.net/5I), I knew I had found my native language.
To get a sense of the tradeoffs taking place that leave you with a noticeably slower UI, see here: https://www.forbes.com/sites/tomgroenfeldt/2019/02/12/openfi...
PSA: It may be a good idea to hire a programmer and customize your software. TT has a nice API. If you have idiosyncratic workflows or views, or if you just want a few particular things to be faster, it's not too hard to use this API to make the tradeoffs and optimizations that work best for your own supplemental UI screens. We did this with a F# + WPF UI where the fill feed and responsiveness was just as snappy as TT's own UI (the old, c++ one).