Toasty, I was worriend about the nearly five and a half year age gap, but so far this is the least of my problems. My sons have always interacted very well with each other. No rivalry since not in direct competition. Older son lets younger son play with all his toddler toys, like his Brio train set, without a backward glance. They love finding some common ground and the possibilities for this are increasing as my younger one grows up. eg: having splashy baths together, copying words and sounds, taking their 'wheels'( bike and pushalong tricycle)to the park.
Also, I do not have to watch my older son every second of the day, and I can even give him some responsibilities eg carrying the nappy bag the car, holding his brother's hand as we walk, which is helpful.
The main problem for me is the loss of freedom. You see all your one-child friends getting their lives back a little, but you're plunged right back into toddlerland: When you host a sleepover, you know that the parents are having a child-free evening and morning. When my oldest gets invited to a sleepover, I still have the youngest to care for. Also I can't meet up for joint visits to the cinema, or even pop round for a long home visit, because my toddler is not going to quietly amuse himself in the same way that my older son now can.
But, having been through it once, you know how quickly your child grows up, so you can enjoy each stage a little more.
If you can find the thread I mentioned earlier, there are more postings about the pros and cons of having a second child.
Hope this helps!