Advice needed for interim graphics card upgrade

Hi. I currently run FSX Gold on an 8 year old system. Ultimately I would like to fly P3D v4, but for this I will need a completely new rig, and that is unfortunately not financially possible this year. I am looking for an interim upgrade to last me the next year or so. 

My current system is a Dell, running W7/64 on an i7 860 @ 2.80 GHz with 8 GB RAM and an OEM GeForce GTS 240 with just 1 GB graphics memory. My FS setup includes ORBX Global Base, Vector & OpenLC, Pilot's Global mesh, REX, ASN, plus a couple of study sim level aircraft and several high end airport sceneries (ORBX, Flytampa, Taxi2gate, UK2000, Aerosoft). I run FSX on DX9. You will appreciate that my current system struggles from time to time. When in the air I can usually get 20-30 fps, but on or close to the ground I might get only 10 fps (or lower), and this is with sliders set at a sensible level.

I am looking to upgrade my graphics card to try to squeeze a few extra fps out of the system and get it to run more smoothly. I am very well aware that FSX is very CPU dependent - I read somewhere that it is around 75% CPU and 25% GPU. My CPU cannot be overclocked or upgraded. So I am not expecting miracles from a GPU upgrade, but if I can get a small improvement to make things smoother, that would be a success. My current PSU is 350 W. I really need to get more graphics memory, as 1 GB is too little with the addons that I have. Should I aim for 4 GB, or would 2 GB be sufficient for my setup?

I have seen EVGA GTX 1050 2 GB at a reasonable price on Amazon, and I think this would fit my PC case. According to the EVGA web site it needs minimum 300 W (but does add that this is based on an i7 3.20 GHz, which is just slightly higher than my specs). Should I change to a more powerful PSU? Can I do this using the same motherboard? Some 4 GB cards I have seen will need at least 400 W, so I need to work out whether this would be feasible for me.

As this will be just an interim upgrade, I do not want to spend the earth (and cannot afford to anyway), so I am just looking for a modest improvement. Thank you for any advice you can give. 

Adrian