Power usage when mining LTC compared to BTC/PPC? Can't measure it myself!

Hi all! I've been mining and lurking around these forums for a while, and have finally decided to make an account so that I might get an answer to a question I've had for a while now. I'd already had my PC with a HD 5870 for a while before I started getting into Bitcoin a few months ago, so there's never been any need to mine to get a return on any kind of investment. The only costs associated with mining cryptocurrencies for me is the electricity; just so happens that, despite living in the UK, where electricity costs seem to be higher than in the US, I do mine more in £ than I (read: my dad) pay for electricity, thanks to the 5870. Not too long after first getting into Bitcoin, I read about Litecoin, and after some hesitation, switched to that instead, simply because of the fact that, on paper at least, I can mine more BTC (in terms of LTC) than I would do just mining BTC from the start. I stuck with mining LTC for a while.

Recently, PPCoin was launched, and after some MORE hesitation with adopting a new cryptocurrency (I can't pretend that I understood, or understand, in much depth any purported advantages that PPC claims to offer and whether it would lead to any kind of significant adoption), started mining it after the Bitparking PPS pool was launched. Switching back to a SHA256 coin, and the different GPU clock tweaking tactics that came with it, made me wonder if the extra power used mining LTC because of much higher memory clocks, fan speeds etc. actually NEGATE the on-paper profitability of mining it compared to BTC or PPC. I've only just started undervolting slightly in addition to overclocking the core (I'm willing to sacrifice some energy efficiency for getting rewards quicker!) and underclocking the memory - undervolting may well be possible when mining LTC, but I doubt to anywhere near the same extent if it is.

Does anyone have any idea how much in terms of wattage (or maybe in relative terms seeing as not everyone has the same card) can one save when mining BTC/similar coins compared to mining LTC, and does anyone think the power saved by mining BTC (or PPC, seeing as it is, according to Coinotron, more profitable to mine than BTC at the moment) with the appropriate over/underclocking strategies would actually make mining them MORE profitable than mining LTC? I'd work it out myself, but I don't have anything to measure my power draw! Using the calculator at allchains.info with fees of 2.5% for BTC and 4.8% for LTC AND estimates of power usage (430W for BTC, 450W for LTC... I might be well off, lol) suggests that LTC is still more profitable; BTC only starts becoming more profitable if power usage is 390W, which sounds a bit unlikely, but there would surely be more room for power usage if mining PPC at current difficulty and prices. Thanks in advance for any help! This is probably going to be a rather difficult post to read...