Split,
as I read this (sorry if I misunderstand) is that you are going to limit your spread bet to ensure you only risk as much as if you were holding the actual shares - you can't do that, as the gap (ergo the loss) is geared then 'the equivalent holding of actual shares' in the event of (say) a $5 gap is different to the number of shares you'd have to get the same effect as a $7 gap - you don't know how big the gap will be, you therefore can't work out the equivalent share holding in advance. All you know is that once the gap has appeared then you are £X down. (Or up, if lucky <g>).
Sorry if I misunderstood the point you made, that's how I read it?
Euro - trading involves a rational assessment of risk:reward, my point is that whilst trading intraday is fine, you have no control over any position held overnight - for a significant period of the day the stocks are trading without you being able to react to what is happening (both out of hours AND ifor a short period in normal market hours when at least some SB companies don't allow you to trade them).
If you hold shares, and have several on the go simultaneously, then the worst that happens is you lose one part of your portfolio (Railtrack event) or more often a profit warning hammers one part of your portfolio for perhaps 50% - if you had say 6 shares on the go at the time that's maybe 8-9% of your funds down the swannee. This would be somewhat annoying, but recoverable. If your spread does the same then even on quite 'cheap' shares you are down a 3 figure sum, perhaps up to £1500 at minimum stakes.
Now that, for most SBers, would be a significant hit - I'd suggest for many it'd wipe them out. (For all the hype on here, how often do you read 'I opened the account with £100 to try it out...' etc?) At the very least those wondering at the original question regarding holding overnight positions can now decide if their accounts could stand dropping a few hundred overnight becuase they held?
It's NOT a case of 'too risk averse' - I've watched a couple of large US companies gap down in the last fortnight, this is from less than 60 shares the SB company actually accept daily bets on, the bigger drop was $7.30 or £730 if you had minimum bet the wrong way at the time. I had been trading that share until exiting prior to the close, and was hoping to make approx £25 from it. Risk:Reward is essentially meaningless in such a case - you can only claim to be taking risk:reward into account if the market is open and you can exit so you have some control over your entry and exit prices - with a market that can close and move against you in a highly leveraged manner it is pure delusion to assume you can calculate risk.
How can you minimise risk when you are losing £1+ per cent of the underlying, and you can't exit until the SB company start time? You don't control risk at all, nor can you forecast it - all you can do is say 'it probably won't happen'. Gaps occur often enough for some TA traders to focus on them as a pattern to trade, they're far from infrequent - whilst a smallish gap will just cause some pain, a larger gap could well result in a margin call.
Guaranteed stops I asked Cap Spreads about on T2W some time ago - their answer was (basically) these cost the punter more, other companies don't allow you to set them close enough to be worth having anyway. It seems to me that the SB companies are simply saying they don't want you to be able to limit losses whilst letting winners run, and sensibly I can't blame them for that. Actually I just can't imagine an incentive for them to come up with a sensible loss limitation option - I suppose you might argue that they'd clean up and steal market share etc but I suspect the impact on the bottom line would be negative.