There are simply too many possible problems - you really need to pin them down one at a time.
First is to make sure all of your EFI settings are correct, and doing what they need to do.
Second is to do a completely fresh install of Win7 - and I mean, completely fresh, not just some gloss over.
Third, you are attempting to run Win7 Ultimate 64-bit on a measily 4GB of memory - that will throttle it back pretty heavily. I would say that 6GB is sort of a "minimum" for 64-bit Ultimate, while 8GB will let you actually run software.
Once installed, I would test before installing software. The HDD can be a limit with say, loading times, or read/write times - but for regular running, should not be a factor. I'd test the system with something like Prime95, where the HDD is not a factor at all, and shake down the system that way. Going to an SSD will perhaps improve boot times, or load times of software, but will not factor into the meat of the performance, which is calculations.
I would reinstall all software from fresh, because their can be problems if you simply try to reuse previously installed software, especially if there are differences in drivers and so forth. Same if the change also brought about a change from 32-bit to 64-bit - there could be a lot of brain damage caused by old 32-bit software running on a 64-bit system, with major performance hits.
Also, you should be realistic when it comes to "performance", because unless your Phenom x2 was say, a 2GHz model - really, something like going from a Phenom II at 3.2GHz to an i7 at 4GHz won't be that earth shattering, especially if you are not using software that uses multiple cores or multile threads.
It is also possible that the HDD is on it's way out - you should use proper testing software to evaluate it, rather than relying on some lame "benchmark" that is specious at best, and does zero actual tests on the drive itself. However, a HDD that is impeded will only impede load times, or times then the OS is forced to swap - like on a Ultimate 64-bit system that only has 4GB of memory, which is the "bare minimum", coupled to a defective drive...