Hello Martin,
SP3 is a wonderful machine but like anything else has room for improvement (hence why we expect SP4 as its next iteration). Personally I do not expect SP4 to be a significant leap forward from SP3; in fact I'd expect SP4 to be inferior in some respects such as processing power since the near-credible speculations about SP4 (as none of the rumours have been confirmed by Microsoft) have more to do with a fanless design with improved battery life - the Broadwell cpu being the drive behind this. Fanless means throttling back the clock rate to avoid over-heating. Lower clock rate is also an effective means for better battery life, in addition to other low battery techniques and technologies, be it in hardware and/or software. Hence an interesting law of physics at work here for increasing the clocking rate (for processing power), keeping the machine cool, and prolong the battery life. Not easy to attain one without negatively offsetting the other(s) with existing ic technologies. Therefore why I do not expect increased processing power from SP4 every other things being as SP3.
Assuming the processing power is about the same as SP3, perhaps the question could be - what is the deal breaker for not getting SP3 now?
- are you put off by the occasional fan noise and moderate heat dissipated by SP3?
- is the single USB3 port a deal breaker for you (assuming SP4 will overcome this limitation)?
- assuming SP4 provides mobile/cellular connectivity with LTE integration, would you consider such future-proofing as a significant investment?
- SP3 being of significant cost, can you afford to wait for SP4 for better cost-benefit analysis that better fits your needs?
On the last point, I expect SP4 to be slightly cheaper or about the same for similar major specs (RAM and disc storage sizes, bar LTE) but I could be wrong.
If the above points are not in the forefront of your thoughts (and you find a good deal on SP3) go for it. I would not consider SP4 to easily over-shadow the SP3 with its considerable processing power and beautiful design.
-- dave