CPU/GPU upgrade recommendations

I currently have a i5-3570K that I've overclocked to ~4.3 ghz, alongside a GTX 670 that I've slightly bumped the speeds up on as well. I've had this setup for a few years now, and overall I'd say I'm happy with it, FSX is pretty smooth under most situations. However, there are certain scenarios/locations and aircraft that can cause some frame rate issues, and I'd like to know if certain upgrades would be worth it to help.

There are two main things that occasionally cause frame rate issues for me (as in below 20, it's usually "smooth enough" above that):

1. Lots of clouds. I do love me some ASN overcast. Occasionally, really thick overcast layers or lots of cloud layers will cause a noticable loss of FPS.

2. Certain complex aircraft together with scenery-dense areas. For example, Ifly 737 and FSLabs Concorde at UK2000 EGLL.

I would imagine that #1 would be mostly GPU related, while #2 is primarily CPU-limited, correct? Does anyone see any clear opportunities for improvement with a CPU and/or GPU upgrade? If, so, could I have recommendations? The ideal would be to have things like FTX Global and FTX Vector installed, with all FSX settings maxed out, and not have to worry about frames dropping below acceptable levels or the terrain going all blury because the CPU or GPU can't keep up. As I said, this is the case most of the time, but certain areas and certain situations can bring my rig back to earth and kill the immersion.

thanks