Pompey are preparing to face two of their biggest rivals for promotion into the Championship.
They pay a visit to Barnsley this weekend before hosting Sunderland in the final fixture before Christmas.
Both suffered relegation from the second tier last term and are well-placed to go straight back there.
But it is Kenny Jackett’s men who currently top the table and he is looking forward to a couple of tough tests.
The Blues boss said: “They’re great games, with both sides having come down from the Championship and reacting positively to League One.
“They’ve been able to keep their squads together, build again and are doing everything they can to bounce back.
"At the moment I’m not sure how big the gap is between this league and the one above – but I’d like to find out."
“I’m sure both will be there or thereabouts at the end of the season, but there are a lot of good sides towards the top of this division. We’re pleased that we’re in that mix.
“Barnsley have got the likes of Kieffer Moore and certainly look a force. The players they’ve got make the statement that they only want to be here for one year.
“At the moment I’m not sure how big the gap is between this league and the one above – but I’d like to find out.
“All we can do currently is focus on the level we’re at, which is very strong and there’s plenty of competition.”
Snow is currently forecast for South Yorkshire this weekend, but Jackett will not be doing anything different.
He said: “It generally gets pretty cold the closer you get to Christmas and especially in the north, so it certainly won’t be unexpected.”
Ben Thompson can feature against the Tykes after having his midweek red card overturned and Jackett is close to having a full contingent to choose from.
He said: “Dion Donohue’s available and is very positive about putting pressure on those players who are currently in the side.
“David Wheeler is not too far away and aside from that, I’m pleased to say that we’ve got a clean bill of health.”