There is no such thing as a 9700x.
I think you mean't the 9800X.
The 9800X is acceptable chip and seem to be on sale for a good price here:
Buy Intel Core i7-9800X 3.8 GHz Eight-Core LGA 2066 Processor featuring 8 Cores & 16 Threads, 3.8 GHz Clock Speed, 4.5 GHz Maximum Turbo Frequency, LGA 2066 Socket, 16.5MB Cache Memory, No Integrated Graphics, Supports DDR4 Memory, Supports Intel Optane Memory, Supports up to 44 PCIe Lanes, 9th...
www.bhphotovideo.com
So if your asking me:
10900x has 48 pci-e lanes
9800x has 44 pci-e lanes
How many additional cards / nVME / GPU's does your system have or intend to have?
Is it worth the extra 200 dollars for +4 pci-e lanes on the 10900X?
As for gaming performance, they both turbo well into the 4.5-4.7ghz territory on stock settings, which is more then acceptable unless your a FPS counter and like seeing over 9000 fps. (exaggeration, but you get my point).
If your gaming at 1440p or 4k, your going to be GPU bound anyhow unless you got lucky in fighting bots, and somehow scored a RX 6800XT or a 3080/3090.
If your really really tight on budget, i would look on ebay for a i7-7740x. These are 4c/8t processors, but only half your ram slots will work.
They are very limited in pci-e lanes, but they are excellent overclockers and excellent gaming cpus.
Infact i had one ramped up to 5.5ghz for lulz and it didn't even break a sweat.
But again, its majorly limited in the pci-e lanes and memory chanel being dual and not quad like on the other higher end i9's.
So my overall recommendation...
If you already have the quad channel ram (4 sticks of identical ram), try to get the 9800X as it will be future proof for a few more generations as AMD seems to pop new cpu's like candy and its really hard to not get buyers remorse on AMD.
At least this way you can wait to see what happens on threadripper side for settle, before you go over to the AMD ship.
If you have only 2 ram sticks go on ebay and try to secure a i7-7740X. They should only run you 200 or so dollars, and should hold you out until you can secure a Ryzen 7 system later on should you go that route. But again, the 7740X route is very short lived, so i would not recommend this unless you intend to upgrade soon, and would recommend the 9800X route.
I recommend the 9800X route, as the price is just more competitive to the 10900X unless you absolutely need those extra 4 lanes.