To overtake or slipstream? That is the question. Whether tis a breach of ettiquette to do either when cycling at similar pace.
Also . . on communication. Body language. Vehicle language. Smile, motion and vocalise.
Perfectly justified to slipstream I think especially if overtaker slows down a bit. Also can be an opportunity to take a rest. :-) If pace too slow just speed up and overtake. Agree one should be able to put in a good +5-10% more speed before overtaking. Nothing wrong with a friendly word of communication in warning or in case of pausing together at junction. My regular commute home has a steady rise from Dublin city centre and I find there is quite a variety in pace with a good few slower cyclists, some of similar pace and the odd few extremely fast people.
When catching up with someone of similar speed I find you cannot do anything but latch on. It is that or go for overtake. If latching on then do so loosely watching well ahead of other rider, riding defensively. I would ride in line a little outside other rider protecting from overtaking traffic but move back in if front rider has to negotiate hazard ahead or someone faster comes up behind. I would be reluctant to overtake and cause inconvenience unless I could be confident of getting well away and relieving the overtakee of the sight of my rear end!
I'm quite Zen I think (and modest about it too ;)) if being overtaken or with cycling and driving generally. Car, bike or motorbike. But got to admit there's something nice and warm smugly satisfying about leaving someone (safely!) for dust if they have impinged on ettiquette. I ride a MTB no pedal clips so I don't look the fastest if not moving. Half the time in mad shorts instead of cycling gear. So beware ;-). MTB tyres so I can bash over potholes cracks cobbles manholes up down bike lanes of course. I'm much faster on my wife's slick tyres - on the straight! But I have found you have to reduce speed more to take corners! These discoveries keep us somewhat humble. But not too humble. I hope.
One thing I find with communication is maybe we could do a bit more. A lot of cycling catching up, cycling behind, passing is done without a word. With defensive driving we read others intentions by body language of other vehicle and car. But with encountering other cyclists - especially if they look like they are less confident - I think it helps if you can vocalise intentions sometimes. e.g. "*ahum* I'm - er - just going to come up on your right there." when you have space to move out but want to not scare someone. Also at junctions I would give way to pedestrians. ESPECIALLY if they have the right of way! :-) I find signalling this with showing palm forward arm out bent at elbow (like garda stop traffic signal - not the closer to body I intend going straight signal) leaves pedestrians know you are stopping also leaves bikes and traffic behind know you are giving way. Pedestrians less hesitant and happier and clear junction faster and safer leaving way clear. Yay. Win win. Making eye contact is great for defensive driving and riding and played like the kids sweet/sour game is good fun. Most people pedestrians cyclists drivers all turning out to be sweet :O)