Assume (1). Since $\Hom_{D(\mathcal{O}_X)}(G[-i], E) = \Hom_{D(\mathcal{O}_X)}(G, E[i])$ we see that this is zero for $i \gg 0$ by Lemma \ref{lemma-ext-from-perfect-into-bounded-QCoh}. This proves that (1) implies (2). \medskip\noindent Parts (2), (3), (4) are equivalent by the discussion in Cohomology on Sites, Section \ref{sites-cohomology-section-global-RHom}. Part (5) and (6) are equivalent as $H^i(X, -) = H^i(R\Gamma(X, -))$ by definition. The equivalent conditions (2), (3), (4) are equivalent to the equivalent conditions (5), (6) by Cohomology on Sites, Lemma \ref{sites-cohomology-lemma-dual-perfect-complex} and the fact that $(G[-i])^\vee = G^\vee[i]$. \medskip\noindent It is clear that (7) implies (2). Conversely, let us prove that the equivalent conditions (2) -- (6) imply (7). Recall that $G$ is a  classical generator for $D_{perf}(\mathcal{O}_X)$ by Remark \ref{remark-classical-generator}. For $P \in D_{perf}(\mathcal{O}_X)$ let $T(P)$ be the assertion that $R\Hom_X(P, E)$ is in $D^-(\mathbf{Z})$. Clearly, $T$ is inherited by direct sums, satisfies the 2-out-of-three property for distinguished triangles, is inherited by direct summands, and is perserved by shifts. Hence by Derived Categories, Remark \ref{derived-remark-check-on-generator} we see that (4) implies $T$ holds on all of $D_{perf}(\mathcal{O}_X)$. The same argument works for all other properties, except that for property (7)(b) and (7)(c) we also use that $P \mapsto P^\vee$ is a self equivalence of $D_{perf}(\mathcal{O}_X)$. Small detail omitted. \medskip\noindent We will prove the equivalent conditions (2) -- (7) imply (1) using the induction principle of Lemma \ref{lemma-induction-principle}. \medskip\noindent First, we prove (2) -- (7) $\Rightarrow$ (1) if $X$ is affine. This follows from the case of schemes, see Derived Categories of Schemes, Proposition \ref{perfect-proposition-detecting-bounded-above}. \medskip\noindent Now assume $(U \subset X, j : V \to X)$ is an elementary distinguished square of quasi-compact and quasi-separated algebraic spaces over $S$ and assume the implication (2) -- (7) $\Rightarrow$ (1) is known for $U$, $V$, and $U \times_X V$. To finish the proof we have to show the implication (2) -- (7) $\Rightarrow$ (1) for $X$. Suppose $E \in D_\QCoh(\mathcal{O}_X)$ satisfies (2) -- (7). By Lemma \ref{lemma-direct-summand-of-a-restriction} and Theorem \ref{theorem-bondal-van-den-Bergh} there exists a perfect complex $Q$ on $X$ such that $Q|_U$ generates $D_\QCoh (\mathcal{O}_U)$. \medskip\noindent Say $V = \Spec(A)$. Let $Z \subset V$ be the reduced closed subscheme which is the inverse image of $X \setminus U$ and maps isomorphically to it (see Definition \ref{definition-elementary-distinguished-square}). This is a retrocompact closed subset of $V$. Choose $f_1, \ldots, f_r \in A$ such that $Z = V(f_1, \ldots, f_r)$. Let $K \in D(\mathcal{O}_V)$ be the perfect object corresponding to the Koszul complex on $f_1, \ldots, f_r$ over $A$. Note that since $K$ is supported on $Z$, the pushforward $K' = Rj_*K$ is a perfect object of $D(\mathcal{O}_X)$ whose restriction to $V$ is $K$ (see Lemmas \ref{lemma-pushforward-perfect} and \ref{lemma-pushforward-with-support-in-open}). By assumption, we know $R\Hom_{\mathcal{O}_X}(Q, E)$ and $R\Hom_{\mathcal{O}_X}(K', E)$ are bounded above. \medskip\noindent By Lemma \ref{lemma-pushforward-with-support-in-open} we have $K' =  j_!K$ and hence $$ \Hom_{D(\mathcal{O}_X)}(K'[-i], E) = \Hom_{D(\mathcal{O}_V)}(K[-i], E|_V) = 0 $$ for $i \gg 0$. Therefore, we may apply Derived Categories of Schemes, Lemma \ref{perfect-lemma-orthogonal-koszul-first-variant} to $E|_V$ to obtain an integer $a$ such that $\tau_{\geq a}(E|_V) = \tau_{\geq a} R (U \times_X V \to V)_* (E|_{U \times_X V})$. Then $\tau_{\geq a} E = \tau_{\geq a} R (U \to X)_* (E |_U)$ (check that the canonical map is an isomorphism after restricting to $U$ and to $V$). Hence using Lemma \ref{lemma-bounded-truncation} twice we see that $$ \Hom_{D(\mathcal{O}_U)}(Q|_U [-i], E|_U) = \Hom_{D(\mathcal{O}_X)}(Q[-i], R (U \to X)_* (E|_U)) = 0 $$ for $i \gg 0$. Since the Proposition holds for $U$ and the generator $Q|_U$, we have $E|_U \in D^-_\QCoh(\mathcal{O}_U)$. But then since the functor $R (U \to X)_*$ preserves $D^-_\QCoh$ (by Lemma \ref{lemma-quasi-coherence-direct-image}), we get $\tau_{\geq a}E \in D^-_\QCoh(\mathcal{O}_X)$. Thus $E \in D^-_\QCoh (\mathcal{O}_X)$.