And such is the fierce competition at the top level of European rugby that even Edinburgh Rugby - the only side left with a 100 per cent record - are not guaranteed a spot in the last eight just yet, although a home win over Neath-Swansea Ospreys this weekend will be enough.
The five sides out of contention are Leeds Tykes, the Ospreys, The Borders, Benetton Treviso and Calvisano. Cardiff Blues, who lost their first three games before stealing a one-point victory over Biarritz Olympique on Saturday, are even in with a shout of the knock-out stages.
The Arms Park side have to secure the maximum 10 points against Leinster Lions and Sale Sharks - as well as hope other results in Pool 3 go their way.
But all eyes remain firmly focused on the fascinating Round 5 matches that could bring either delight or despair. The television cameras will be at seven of the matches, including Sky Sport's delayed transmission from Agen's clash with Northampton Saints after showing Leinster Lions' meeting with Cardiff Blues, on another bumper weekend rich in promise of high quality rugby and drama.
It all adds up to going down to the wire, though Munster and Toulouse are favourites for the title at 3-1 with most bookmakers. Leinster and London Wasps are at 6-1, with Gloucester (10-1) and Llanelli Scarlets (12-1) also supported.