The i7-740QM is still a great CPU. The 1.73GHz is just a base clock, it boosts to 2.93GHz in most gaming scenarios.
Boost clocks are as follows:
2933 MHz (1 core)
2533 MHz (2 cores)
1867 MHz (3 or 4 cores)
Decent enough. However if that doesn't do it for you, there are the i7-920XM and i7-940XM chips with overclocking capabilities. So long as you have the A09 or A10 BIOS from Dell (which you do), you can usually get these guys running at 3.4GHz on all cores, or with a spread from 3.3 - 3.6GHz following the boost pattern displayed above.
The i7-920XM will run you about $120. Here's one on eBay:
http://www.ebay.com/itm/Intel-Core-i7-920XM-SLBLW-2-0-3-2G-8M-Extreme-Processor-CPU-Mobile-km-/311489291405?hash=item488635648d:g:BQwAAOSwiwVWTz0H
Next up you're looking to upgrade the GPU. Going off the CPU and BIOS info, I'm going to guess you have the M17x R2. This is important because the R2 has dual graphics, I.E. CrossfireX or SLI. You could order the laptop without a second card installed, but the board remained the same and you can still install a second card at any time.
IF: You have dual Radeon Mobility HD 5870s, that's actually already pretty good. However the Radeon HD 6970M, or GeForce GTX 675M are both huge increases in performance. Two of either in SLI/Crossfire would very quickly stack up to modern graphics.
IF: You have a single Radeon Mobility HD 5870, go straight to a Radeon HD 6970M, GeForce GTX 675M, or put all your money into a Radeon HD 7970M (provided you can find one from a reputable seller).
Upgrading from a single GPU to dual may require the purchase of the GPU interconnect cable, and the second heatsink for the card.
Hope that all helps.
Quick Edit:
For the people telling you to go with a desktop, the M17x R2 is one of the most flexible, upgradeable, and powerful laptops you can buy for under $1000. Upgrading it for $300 - $350 puts it WAY AHEAD of any APU system you can build for the same amount of money. Honestly, along with the Sager NP8150 the M17x R2 is a fucking great machine and with an i7 Extreme + dual graphics will continue to be one of the best gaming laptops for the money.
Oh yes, and with a few BIOS tweaks the M17x will support the GTX 980M.