Any way of speeding up a pc with reasonable specs?

This is NOT a serious problem, just more of an annoyance which is intriguing me.
With 4gb ram, a reasonable dual processor and graphics card, one would expect a reasonably good performance whatever the case.
My automatic startup consists of just Avast AV, Java, and Malwarebytes although l also get additional icons on the taskbar for the Network and Sharing Center and Action Center.
I use Firefox as my main browser.
I also use SuperAntiSpyware, CCleaner, and Defraggler reasonably frequently, so l know that my system is clear of any junk, malware, spyware, and that no viruses are present.
I fire the system up in the morning, bring up Firefox and all is fine, and reasonably quick.
Do a fair amount of downloading using the MiPony download manager to access rapidshare files, but with my crap connection, the max download speed seems to hover around the 280kbs mark.
I may also have two FF sessions on the go, as well as the downloading, so whatever l do after that seems to really slow the system down.
I have even run ConvertX at the same time as all of the above and the system came to a near grinding halt.
Now l know that all of the above are processor/ram hungry but surely with my specs the computer should more than cope?
Maybe l'm missing something obvious or my dual processor system just cannot cope with more than two ram hungry programs running at the same time.
Has anyone got any ideas or do l just have to live with it.

Blimmin' heck Brink, only a mere 33 checkpoints to go through (ha ha).
Thanks very much for the quick response, it's really appreciated.
I'll go through each one in turn and see what the results are after number 33.
Regards

Sorry Brink and Pparks1 as l usually reply to posts quicker, but have been a bit tied up.
Most of the things listed l do anyway, but am just tinkering around with the pagefile at the moment. Doesn't seem to make that much of a difference, but then Windows 7 normally handles this effectively anyway.
A clean install will no doubt make a difference, as when l first installed W7 it whizzed along. Then l would have to bring back everything l have at the moment and after a while, l'll probably be back in the same position as of now.
The SSD option seems interesting but due to lack of funds at the moment, basically none, will leave this one open for now.
One thing l have noticed is that Firefox seems to be a lot slower. When l load FF, down the bottom of the screen just above the taskbar it flashes up the standard messages of "transferring data", "waiting for" etc.
Some of the "waiting for" data seems to take a long time to load but that could just be down to my connection, which isn't the fastest!
Out here in the back of beyond, about 5 kilometers away from the nearest exchange, Speedtest shows a Ping of 81ms, a download speed of 2.59Mbps and an upload speed of 0.14Mbps. This is the best it's going to get unless they upgrade all of the cabling which l very much doubt.
Anyway, as l said, it's not too much of a problem as l'm sort of used to it by now.
Thanks again for you prompt and as ever, helpful replies.
Regards

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Thanks everyone, you have all been most helpful.
I'll bear everything in mind and will close the post for now.
If l get any future problems l know where to come to.
Kind Regards